A novel virus of flaviviridae associated with sexual precocity in macrobrachium rosenbergii

Since 2010, sexual precocity, a typical sign of the iron prawn syndrome (IPS), resulting in the reduced size of farmed giant freshwater prawns Macrobrachium rosenbergii, has caused substantial production losses. However, the cause of IPS was not clear. We ran tests for eight major shrimp pathogens, but none were detected from IPSaffected prawns. We performed the histopathological examination of tissues and identified an eosinophilic inclusion in the perinuclear cytoplasm of cells in various tissues associated with nervous and endocrinal functions in the compound eyes. A subsequent bioassay with viral extracts of IPS-affected samples reproduced the gross signs of IPS. Metatranscriptomic sequencing identified a novel virus of Flaviviridae in all IPS-affected M. rosenbergii prawns, which was not found in samples without IPS. This virus contains a positive-sense, single-stranded RNA genome of 12,630 nucleotides (nt). Phylogenetic analysis of the conserved RdRp and NS3 domains showed that it may belong to a new genus between Jingmenvirus and Flavivirus. Under transmission electron microscopy (TEM), putative virus particles showed as spherical with a diameter of 40 to 60 nm. In situ hybridization found hybridization signals consistent with the histopathology in the compound eyes from IPS-affected M. rosenbergii. We provisionally name this virus infectious precocity virus (IPV) and propose the binominal Latin name Crustaflavivirus infeprecoquis gen. nov., sp. nov. We developed a nested reverse transcription-PCR diagnostic assay and confirmed that all IPS-affected prawns tested IPV positive but normal prawns tested negative. Collectively, our study revealed a novel virus of Flaviviridae associated with sexual precocity in M. rosenbergii.